1. Field of the Invention
This invention relates to a boat hull having a bow, a stern, and a keel along its bottom extending from the bow toward the stern and more particularly to a tunnel structure along the bottom of the boat hull in the form of a truncated hollow partial cone and extension indentation parallel to the keel of the boat. The cone indentation has a central axis that is aligned parallel to the keel of the boat in the bow to stern axis of the boat and at an angle downward from the lay of the keel from the bow to the stern of the boat. The cone indentation begins near the apex of the cone and extends at a constant cone angle toward the stern of the boat to the position of a propeller within the cone and then extends from the position of the propeller at a constant radius from the cone is axis to the transom where the base of the indentation is secured to the stern or transom of the boat hull. The partial cone shaped tunnel accommodates the rotary propeller of the boat, and is truncated near its apex where, at that location, it is attached to the keel of the boat and provides a step through which the propeller shaft to the propeller passes from the interior of the boat.
The present invention is an addition to and improvement on the hull shown and claimed in my U.S. Pat. No. 6,544,081, issued Apr. 8, 2003 for BOAT HULL WITH TUNNEL STRUCTURE.
2. Description of the Prior Art
Prior art patents have disclosed the use of tunnel shapes along the keel of a boat for several different purposes. Stuart, U.S. Pat. No. 3,515,087, discloses a hull tunnel that smoothly increases in size and diameter as extending aft to open fully at the stern. Stuart, U.S. Pat. No. 3,626,894, discloses a tunnel in the bottom of the boat that extends aft of the propeller a short distance with a gradually enlarging cross-sectional area preferably formed by diverging sidewalls of the tunnel. Fisher, U.S. Pat. No. 3,745,963, discloses a tunnel structure designed to converge water flow and increase water pressure aft of the propeller. Shirley, U.S. Pat. No. 4,392,448, discloses the prior art structures intended to produce desireable wake patterns for water skiing. Whitehead, U.S. Pat. No. 4,609,360, discloses a tunnel having a section aft of a propeller with side surfaces that widen the tunnel toward the transom. Hankley, U.S. Pat. No. 4,622,061, discloses a tunnel with a wedge postioned in the tunnel aft of the propeller. All of Hankley's wedges reduce the tunnel diameter aft of the propeller and along the sides of the tunnel. The prior art has not directed the hull design to the desire to increase the efficiency of the drive from the boat's motor to the propeller and aft of the propeller through the hull and to increase efficiency of driving the boat into a planing attitude.
In an inboard powered boat, it is desireable to have the axis of the propeller shaft as near as possible to parallel to the keel of the boat. It is also desireable to place the driven propeller in its most efficient alignment with the water surface during initial acceleration and after the boat has attained its planing attitude or speed. The prior art has not addressed the angle of the propeller shaft exit from the hull of the boat and the angle of the propeller shaft to the hull of the boat at the position of the propeller when in driving contact with the water. Further, where boat hulls have been provided with bottom concave depressions, those depressions have not been designed to increase the efficiency of the propeller drive forces aft of the propeller blades to raising the stern into a planing attitude.